After use in examination, therapy, and surgery, steel medical instruments such as scissors, forceps, and tweezers and hard and soft endoscopes are dirty with blood or body fluid or the like. Due to a possible contamination of the dirt with a pathogenic protein, such as abnormal prion, bacterium, or virus, such a dirty medical instrument should be certainly cleaned, sanitized, and sterilized to be reused. It is said that, in cleaning of a medical instrument, sanitization and/or sterilization are less effective by insufficient washing and remaining dirt than expected, resulting in imperfect sanitization and/or sterilization. In addition, a remaining protein after a step of cleaning is denatured with a sanitizer such as glutaraldehyde or peracetic acid or a disinfecting treatment with high-pressure steam or ethylene oxide in a next step to become stubborn dirt that is very strong and hard to be removed.
In clinical practice, a cleaning result of a medical instrument with these cleaning agents is generally visually examined. A medical instrument still having visible dirt will be cleaned again. However, a recent study reported that most of medical instruments used in clinical practice had no visible dirt by being cleaned with a commercial neutral enzyme detergent or an alkaline detergent, but these were then fluorescently-stained and thoroughly examined with a fluorescent microscope, there was still protein dirt fixed on these instruments (Journal of Hospital Infection (2008) 68, 52-58).
Neutral and weak alkaline dilutions of neutral enzyme detergents have been conventionally used as a medical instrument cleaning liquid that can remove protein dirt.
JP-A2001-31999 describes a method of cleaning with a neutral or weak alkaline enzyme detergent. The method of JP-A2001-31999 unfortunately has a problem of conflicting effects of an alkanolamine that is necessary for achieving a sufficient detergency but causes corrosion of light metals such as aluminum. Very expensive medical instruments like as an endoscope should never be corroded by cleaning.
JP-A02-45599 and JP-WO9-512586 each disclose a cleaning liquid containing an ionic surfactant together with a nonionic surfactant, an alkanolamine, and a protease. The addition of the ionic surfactant, in one hand, provides a relatively high detergency, but on the other hand, problematically causes heavy foaming during cleaning in a medical instrument washer and much foam overflows a cleaning tank or decrease the propagation of a physical force, such as of water stream and ultrasonic wave, to the medical instrument to result in a decreased detergency to an insufficient level. A reduced amount of the ionic surfactant results in a reduced amount of foam but also a reduced detergency to an insufficient level. To enhance the detergency of a cleaning liquid of such a formulation, the alkalinity of the cleaning liquid may be increased, but an increased alkalinity causes a problem of corrosion of light metals.
JP-W2008-530279 discloses a detergent composition containing a detergent for medical instruments and an anti-corrosive substance. But the cleaning method of the publication has an insufficient detergency to fixed blood stains and besides has a difficulty in perfect prevention of generation of a residual metal salt derived from the anti-corrosive substance. The detergent composition of the patent is therefore hardly applicable to cleaning of a medical instrument that is inserted in the body and required to rigorously ensure the safety thereof.
JP-A2008-133340 discloses a liquid detergent composition used in an automatic dishwasher, that contains a water-soluble solvent selected from glycerol, ethylene glycol, and propylene glycol, an enzyme, a water-soluble calcium salt, an alkanolamine compound, and water.